"Author" vs "Writer" prefixes

Background Pony #C170
Well, for example, it could be relevant for comics, for images with stories as text in the image, or stories in the description, or to refer to the author of a fanfic (not included) with which the image is associated (as a cover or an illustration, etc.)
Ciaran
ラ・ゼッタ - For supporting the site
Silly Pony - Celebrated the 13th anniversary of MLP:FIM, and 40 years of MLP!
Shimmering Smile - Celebrated the 10th anniversary of Equestria Girls!
Lunar Guardian - Earned a place among the ranks of the most loyal New Lunar Republic soldiers (April Fools 2023).
Crystal Roseluck - Had their OC in the 2023 Derpibooru Collab.
Flower Trio - Helped others get their OC into the 2023 Derpibooru Collab.
A Lovely Nightmare Night - Celebrated the 12th anniversary of MLP:FIM!
Princess of Love - Extra special version for those who participated in the Canterlot Wedding 10th anniversary event by contributing art.
Tree of Harmony - Drew someone's OC for the 2022 Community Collab
Elements of Harmony - Had an OC in the 2022 Community Collab

Senior Moderator
友情は魔法だ
I honestly didn’t even notice they existed. They seem to be used either to identify the author of a fanfic the the image is for or based on, or on some really old text posts, to identify the person who wrote the text. Either way, they aren’t a part of the site’s copyright processes, so they don’t have any ‘official’ use here. Having both doesn’t seem to seem to be a problem, though.
wdeleon
Princess of Love - Extra special version for those who participated in the Canterlot Wedding 10th anniversary event by contributing art.
Non-Fungible Trixie -
Twinkling Balloon - Took part in the 2021 community collab.
Magical Inkwell - Wrote MLP fanfiction consisting of at least around 1.5k words, and has a verified link to the platform of their choice
Friendship, Art, and Magic (2020) -
Artist -

The difference is that an author is the person who comes up with and directs the substantial idea, plot, and content of a story.
 
A writer is anyone who writes the text. They aren’t always the same as an author because they might be writing the specific text but under the direction of someone else who’s actually coming up with the ideas driving it.
 
Don’t know if this matters in practicality, since I don’t think it comes up much as a distinction in most pictures of characters writing.
Princess Luna
Preenhub - We all know what you were up to this evening~
Thread Starter - Started a thread with over 100 pages
My Little Pony - 1992 Edition
Notoriously Divine Tagger - Consistently uploads images above and beyond the minimum tag requirements. And/or additionally, bringing over the original description from the source if the image has one. Does NOT apply to the uploader adding several to a dozen tags after originally uploading with minimum to bare tagging.
Cool Crow - "Caw!" An awesome tagger
Economist -
A Perfectly Normal Pony - <%Nebulon> Yeah, just fetch me a smaller anus, sweetie.
Magnificent Metadata Maniac - #1 Assistant
From the Night -

Senior Moderator
Site Developer
Tag Czar
I think normally “author” should be used as the prefix. “Writer” is more for works with multiple authors broken up by role, to distinguish the role, to my understanding.
Interested in advertising on Derpibooru? Click here for information!
Ministry of Image - Fanfiction Printing

Help fund the $15 daily operational cost of Derpibooru - support us financially!

Syntax quick reference: **bold** *italic* ||hide text|| `code` __underline__ ~~strike~~ ^sup^ %sub%

Detailed syntax guide